Add Tags to Neutron Resources

给一个network加上tag，用来：

1. Ability to map different networks in different OpenStack locations to one logically same network (for Multi site OpenStack)
2. Ability to map Id’s from different management/orchestration systems to OpenStack networks in mixed environments, for example for project Kuryr, map docker network id to neutron network id
3. Leverage tags by deployment tools
4. allow operators to tag information about provider networks (e.g. high-bandwith, low-latency, etc)
5. new features like get-me-a-network or a similar port scheduler could choose a network for a port based on tags

PUT /v2.0/networks/{network_id}/tags/{tag}

http://docs.openstack.org/developer/neutron/devref/tag.html